This invention relates to an optical waveguide having a refractive index distribution in the propagation direction of light and a method for fabricating such waveguides.
With the development of techniques of optical fiber communication, optical devices have been required to have the capabilities of mass productivity, high reliability, non-adjustment of coupling, automatic assembling, low-loss, etc. To this end, in recent years, optical waveguide type optical devices have become more widely used.
Previously known optical waveguides constituting waveguide type optical devices are shown in FIGS. 17a and 17b, as disclosed in Oohara and Kimura, "OPTICAL COMMUNICATION", page 142, Nov. 1981 published by Corona-sha. These optical waveguides have a stepwise or continuous refractive index distribution in the thickness and width direction but have a fixed refractive index distribution in the propagation direction of optical signals.
Since all the optical waveguides as shown in FIGS. 17a and 17b have a fixed refractive index distribution or (property) in the direction of light or optical signal beam propagation, i.e. in the longitudinal direction of the optical waveguides, they have a disadvantage of the absence of the capability of converging or diffusing the optical signal beam with the propagation thereof. In order to overcome such a disadvantage, it has been proposed to provide a lens as part of the optical waveguide. However, such a lens is required to have a reduced aberration and a desired focal length and also it has been very difficult to attain good controlability in making it. Thus, the prior art waveguide type optical devices are inferior in their optical property (propagation loss, isolation between the channels, etc.) to the optical devices assembled by individual optical components.